Continuous, twenty-four hour or longer, electrocardiogram (EKG) monitoring (Holter) systems are widely used in the prior art for diagnosing heart disease. However, the long term prior art EKG monitoring systems are concerned only with EKG signals which is a major shortcoming.
There is another much simpler diagnostic means used in the prior art, namely the brief exercise "stress test" in which the EKG is recorded during a brief time interval while the patient is exercising strenuously on a treadmill. However this latter test is not comprehensive because exercise is only one of a number of stresses that can cause EKG abnormalities.
U.S. Pat. No. 4,830,021 which issued May 16, 1989 to the present inventor describes a locomotor activity monitoring system which includes EKG and which involves long term monitoring of the patient. The system described in that patent, unlike other prior art cardiac monitoring systems, uses EKG only incidentally and primarily to monitor heart rate.
There are shortcomings in each of the prior art systems referred to above. For example, the Holter system has no detection/recording capability other than time, EKG readings and a patient marker. The patient maintains a time related diary of such events. At best the approach is qualitative. It is also incomplete, since no data is entered, for example, when the patient is asleep. In essence, there is no objective or recorded evidence of any patient activity.
The cardiac abnormalities which are revealed by the prior art cardiac monitoring systems are equated only to physical activities. However, such cardiac abnormalities may also be revealed by a number of other conditions in the body. Knowledge of these conditions, other than physical activity, which provide detectable cardiac abnormalities is frequently important for determining the proper treatment. As noted above, such knowledge can not be acquired from current cardiac monitoring systems and techniques. Copending application Ser. No. discloses a cardiac monitoring system which in addition to physical activities also monitors such other conditions.
It is well known, for example, that inadequate blood supply to the heart may alter a portion of the EKG known as the S.T. segment. The best known cause of inadequate blood supply to the heart is partial closure of one or more arteries by fatty formations. Limited blood flow through a narrowed artery which is inadequate to meet the needs demanded by exercise is a common cause of such EKG changes. However, normal or slightly affected arteries may produce the same effect due to spasms from emotional upsets which are transmitted to the heart by the nervous system. The prior art cardiac monitoring systems offer no aid in differential diagnosis of this problem. The treatment in the case of clogged arteries is normally surgery, but a vastly different treatment is required in the case of arterial spasm caused, for example, by emotional upsets in relatively normal arteries, or even arteries which are partially occluded.
One objective of the present invention is to provide a relatively simple and practical system which detects and records parameters affecting the cardiovascular system of a subject simultaneously with the recording of the EKG data. Should EKG abnormalities be detected, the system of the invention analyzes and correlates physical and emotional activities of the subject and environmental parameters which could cause such abnormalities.
As pointed out in the Copending Application, external events known to cause cardiovascular problems include: physical stress; work; exercise; temperature extremes and changes; and fatigue. In addition, there are emotional stresses which also can cause cardiovascular problems, and these include, for example, such emotional stresses as real or perceived danger, anger, conflict, and the like.
Since it is impractical for a monitoring system to record indications of all of the parameters set forth in the preceding paragraph, some means for detecting, recording and correlating the parameters with respect to EKG abnormalities is required, and an objective of the present invention is to provide a practical system which uses correlation techniques for furnishing data concerning all of the circumstances set forth above as related to EKG changes. This latter objective may be achieved in conjunction with existing Holter EKG monitoring systems.
In the system of the invention, raw data relating to the parameters discussed above may be detected and recorded together with EKG data in a Holter magnetic tape recorder. Alternately, the raw data may be recorded in a separate magnetic tape recorder. In either event, in the system of the invention, the data is reduced, analyzed and correlated on replay. As a second and preferred option, the raw data may be detected and reduced at the monitoring site, and only pertinent specially encoded parameters recorded in the Holter or separate recorder, with the encoded parameters being detected and cross-correlated on replay. As a third option, raw data may be detected and analyzed at the patient's recording level, encoded in existing EKG format, recorded on an existing EKG channel in a Holter recorder, and detected by existing replay means and translated and correlated with the EKG data. In addition, analyzing and correlating data may be reduced with analyzed EKG data at the recorder level, with only the results being stored in the recorder.
For example, and as described in Copending application Ser. No. (K 3423) a prior art four-channel Holter magnetic tape recorder may be provided, three channels of which may be used to record EKG signals, and the fourth channel used to record time signals and additional patient data in multiplexed digital and other encoded form. This additional patient data may then be stored/analyzed in a digital computer which correlates the data and produces a report which contains, for example, a summary of the EKG data such as heart rate, S.T. level, plots of the data, examples of abnormal EKG activity, and potential diagnosis based on the data. By adding data related to physical and emotional stresses in accordance with the present invention, the specificity and the reliability of the diagnosis and treatment can be increased.
The system disclosed in the Copending application Ser. No. (K 3394), in addition to collecting ambulatory data such as described in U.S. Pat. No. 4,830,021 also collects additional data relating to activities which also affect or define cardiac responses of the subject. As described in Copending application Ser. No. (K 3394), these additional activities may include, for example, verbal exchanges, evidence of emotional stress arising from verbal exchanges between the subject and others, emotional stress arising from dreams, and other physical conditions such as the posture of the subject, air temperature, ambient light level, elapsed time, and so on. The resulting data is analyzed and correlated in the system of the present invention preferable as the actual report is generated by the system.